41O COMPOUND PRODUCTS. CHAP. I. 



When tannin is subjected to the process of dis- 

 tillation it yields charcoal, carbonic acid, and in- 

 flammable gases, with a minute quantity of volatile 

 alkali, and seems accordingly to consist of the same 

 elements with extract, from which, however, it is 

 distinguished by the peculiar property of its action 

 upon gelatine. 



Varieties. Chemists have enumerated several obvious va- 

 rieties or species of tannin, which seem to be 

 founded chiefly on the peculiar colour of their pre- 

 cipitate by gelatine. The first and purest species 

 is that which is obtained from the seeds of the 

 Grape.* It forms a white precipitate with the 

 solution of isinglass ; and is approximated in its 

 qualities by the tannin of Nut-galls, which is re- 

 garded, however, as constituting a second species. 

 The tannin of Catechu is a third species. Its pre- 

 cipitate by gelatine is distinguished by a tint of 

 brown. A fourth species is obtained from Ptero- 

 carpus Draco, Dracaena Draco, and Calamus 

 Draco, generally denominated Dragon's-blood. A 

 fifth species is obtained from Rhus coriaria or Sumac, 

 by drying and grinding the shoots of the plant to a 

 powder. Its precipitate by gelatine remains in the 

 state of a white magma, or sediment without con- 

 sistence. A sixth species is obtained from the 

 wood of the Morus tinctoria, by means of mace- 

 ration in water or in alcohol. It is precipitated 



* Davy's El cm. of Agri. Chcm, p. 78. 



